Composition and mixing of individual particles in dust and nondust conditions of North China, spring 2002

Abstract

Individual particles were sampled in Beijing during the unusually strong dust storm of 20 March 2002 (DS) and a nondust day (NDS) and in Duolun, Inner Mongolia (DL), on a nondust day. Fourteen elements were measured in 500 particles of each by SEM-EDX. The main components were clay, quartz, calcite, and sulfur. The mineral aerosol compositionally resembled loess. X-Y Plots of SiO 2 versus SO 3 and Al 2 O 3 revealed a central core of clay, with lines radiating outward toward quartz, calcite, salts, and alumina. The core represented externally mixed clay particles, and the lines represented internally mixed clays and other components. Externally mixed particles (mostly clays) amounted to 65% of the total in DS, 60% in DL, and 50% in NDS. Saline minerals contributed considerable amounts of S, P, and Cl, especially in DS and DL, and could have come from dried salt lakes or saline soils in northern China and southern Mongolia. The strongest correlations of the 14 elements measured were within these salts, not within the aluminosilicate elements. Most Ca existed as calcite in DS and DL, but as CaSO 4 in NDS. S was very abundant in many of the particles in NDS, while a few of these were unambiguously pollution S in DS. High CuO and Al 2 O 3 were found in Duolun, probably from nearby pollution sources. Dust storm aerosol can interact with pollution gases and pollution aerosol during transport to Beijing, although such interactions appear to require longer transport times to observe. SEM photos showed that calcite could serve as a substrate for adsorbing SO 2 or sulfuric acid and ammonium sulfate and allowing them to react and produce gypsum or mixed sulfates. Copyright 2006 by the American Geophysical Union.